The 100 Most Cited Psoriasis Articles in Clinical Dermatologic Journals, 1970 to 2012

Jashin J. Wu, MD; Young M. Choi, BS; Wojciech Marczynski, BS

Dr. Wu is from the Department of Dermatology, Kaiser Permanente Los Angeles Medical Center, Los Angeles, California; Young M. Choi is from David Geffen School of Medicine at UCLA, Los Angeles, California; Wojciech Marczynski is from Indiana University South Bend, South Bend, Indiana

Disclosure: Dr. Wu received research funding from Abbott Laboratories, AbbVie, Amgen, Eli Lilly, Merck, and Pfizer, which were not directly related to this study. Mr. Choi and Mr. Marczynski report no relevant conflicts of interest.

Psoriasis is an increasingly common disease that has almost doubled in incidence since the 1970s.[1] Around the turn of the 21st century, tumor necrosis factor inhibitor therapy was developed and has proven to be a very successful therapy for psoriasis.[2–4] The continued monitoring of the safety of these agents,[5,6] the search for new biologic agents,[7,8] and recent insights into cardiovascular comorbidity9 have made psoriasis a “hot topic” in dermatology research today.

One useful method in determining the impact of an article on the scientific community is by performing a citation analysis. Each article that is referenced by another peer-reviewed scientific article is credited a “citation.” Since 1945, the Institute for Scientific Information has recorded the total number of citations for articles in more than 10,000 journals.[10] Often, citation analyses limit their focus to the “citation classics,” those articles that have received 100 or more citations in a specified timeframe.[11–13]

Dubin et al[13] performed a citation analysis of clinical dermatologic journals to identify the most significant articles in dermatology from 1945 to 1990. In their paper, the value of citation analysis was well-described as a study that “emphasizes the impact of works of colleagues and predecessors, recognizes some of the seminal advances in the field of dermatology, permits discourse on the evolution of medical science, reveals insights into the spread of ideas, and satisfies our curiosity about historical developments in dermatology.”

The purpose of the authors’ study was to perform a citation analysis of clinical dermatologic journals from 1970 to 2012, limited to the topic of psoriasis. The authors hope their study will provide the benefits mentioned above to a highly relevant topic of dermatology today.

Methods
The authors conducted a search of the Science Citation Index of the Institute for Scientific Information from 1970 to 2012. They evaluated 24 clinical dermatologic journals, an adapted list from a similar study[14] (Table 1). Their search was limited to the subject category of “psoriasis.” For each journal, every article that had 100 or more citations was reviewed by two independent investigators and included if the topic of psoriasis was met.
From the total compiled list of included articles, those with the top 100 number of citations were further analyzed for the first author’s country and institution of origin as well as the study type (original article, review article, meta-analysis, case report, case series, editorial, educational, guideline, commentary). Original articles were identified as producing novel information and having a clearly stated objective, methods, and results section. The other study types were easily discriminated based on the categorization by the publishing journal or the opinion of the investigator.

Results
A total of 168 citation classics in psoriasis were collected from 1970 to 2012 in the 24 clinical dermatological journals the authors studied. Four journals (Archives of Dermatology, now known as JAMA Dermatology, British Journal of Dermatology, Journal of the American Academy of Dermatology, Journal of Investigative Dermatology) comprised 92 percent of the total number of citation classics (Table 1). Upon assessing the number of citation classics published over time, there was a sudden peak in trend during the time period of 1985 to 1989 (30 citation classics, 4,717 citations), as well as a gradual increase in the 1990s, leading to another peak from 2000 to 2004 (30 citation classics, 4,865 citations) (Figures 1 and 2).

The top 100 most cited psoriasis articles were compiled (Table 2). The great majority of these were original articles (81), followed by review articles (8). The other clinical study types, except for meta-analysis, were also represented by at least one of the top 100 psoriasis articles. The United States (50) and United Kingdom (18) comprised the great majority of countries from which the top 100 articles were produced. Germany was notable for producing nine of the top 100 articles. The remainder of the countries each possessed less than five articles. The University of Medicine and Dentistry of New Jersey (UMDNJ), Stanford University, and the University of Michigan were the leading institutions of origin for the top 100 articles, each having produced five articles. The University of Kiel in Germany was responsible for four articles. The University of Wales and St. Mary’s Hospital, both institutions in the United Kingdom, produced three articles each. The other countries and institutions of origin are also listed (Table 3).

Discussion
It is not surprising that the great majority of the top 100 classics in psoriasis were published in the premier dermatology journals with the highest impact factors. Likewise, it is expected that most of these influential papers would be original research articles that have contributed novel information to the field of dermatology. Half of the top 100 classics were produced in the United States, recognized as the world’s leader in medical research.
The top dermatology programs in the United States, such as Stanford University, University of Michigan, University of Utah, University of Pennsylvania, Northwestern University, Harvard University, University of Miami, University of Texas, Baylor University, and Yale University were noted to have each produced at least two of the top 100 classics in psoriasis since 1970.[15] Especially noteworthy, the University of Medicine and Dentistry of New Jersey (UMDNJ) contributed five of the top 100 classics in psoriasis since 1970. Dr. Alice B. Gottlieb, Chief of Dermatology at Tufts Medical Center, authored all five of these papers, including four as first author.

The authors found that two peaks in significant psoriasis research occurred around the time periods of 1985 to 1989 and 2000 to 2004. At the end of the 1970s, it was observed that renal transplant patients on cyclosporin A significantly improved their psoriasis.[16] This finding initiated a new theory on the pathogenesis of psoriasis, centered on T-cell activation and inflammatory cytokines.[17] Much of the research in the 1980s, therefore, was sparked by the desire to elucidate the immune-based pathogenesis of psoriasis as well as test applicable therapies. In the 30 citation classics from 1985 to 1989, eight of them dealt with the mechanism of psoriasis and 14 dealt with therapies, mainly cyclosporin A and vitamin D3 analogues.

At the beginning of the new millennium, it was discovered that anti-T-cell-directed therapies were much less effective than therapies targeted toward inflammatory cytokines, specifically TNF-? inhibitors (etanercept, adalimumab, infliximab).[17] As evidenced by the results of the authors’ study, the 21st century has seen a surge in psoriasis research driven by the search for new, effective biologic agents. The fact that these articles, published only in the past decade, have accumulated more than 100 citations is demonstration of their significance to the medical community.[18–20]

The authors acknowledge limitations in their study. Although they believe they included a comprehensive list of dermatologic journals, it is possible that they may have neglected an important dermatology journal. It is highly unlikely, though, that any neglected journal would have included one of the citation classics in psoriasis. Moreover, using only the search term of “psoriasis” may not have included every psoriasis article in the Science Citation Index. Again, it is unlikely that the authors’ methodology neglected any citation classics in psoriasis.
The authors believe their citation analysis of psoriasis research from 1970 to 2012 has accomplished the goals described by Dubin et al.[13] By analyzing the most frequent time periods of citation classics, the authors were able to recognize significant advances in psoriasis pathogenesis and treatment. The 100 most cited psoriasis articles highlight the work of colleagues from institutions across the globe. All in all, this study confirms that psoriasis research is a major component of dermatology today, currently in an exciting period of discovery and innovation.

References
1.     Icen M, Crowson CS, McEvoy MT, et al. Trends in incidence of adult-onset psoriasis over three decades: a population-based study. J Am Acad Dermatol. 2009;60(3):394–401.
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16.    Mueller W, Herrmann B. Cyclosporin A for psoriasis. N Engl J Med. 1979;301(10):555.
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18.    Gottlieb AB, Matheson RT, Lowe N, et al. A randomized trial of etanercept as monotherapy for psoriasis. Arch Dermatol. 2003;139(12):1627–1632.
19.    Gordon KB, Langley RG, Leonardi C, et al. Clinical response to adalimumab treatment in patients with moderate to severe psoriasis: double-blind, randomized controlled trial and open-label extension study. J Am Acad Dermatol. 2006;55(4): 598–606.
20.    Gottlieb AB, Evans R, Li S, et al. Infliximab induction therapy for patients with severe plaque-type psoriasis: a randomized, double-blind, placebo-controlled trial. J Am Acad Dermatol. 2004;51(4):534–542.

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